Rotary phase converters..

Ultradog MN

Well-known Member
Location
Twin Cities
A friend of mine has a lathe w/3 phase motor. The original motor control has been changed/replaced so there is only forward. No reverse.
He runs it off a rotary phase converter which does not have any start capacitor/s on it
To start the rpc he hits the switch and kicks a T bar on the shaft with his foot to get it turning. Then all works good.
Somewhere in the back of my head I remember reading that if he kicked the t bar the opposite way so the rpc was turning in reverse it would reverse the lathe motor as well.
Is this true?
Before I give him some quack advice I would like to verify that it is correct.
A guy doesn't need to reverse a lathe too often so this would give him that capability without any rewiring.
What do you elec gurus say?
 
I don't think reversing the rotation of the converter motor would reverse the lathe motor.

That would not be very practical. The most common need for reversing a lathe is threading, backing out a tap or a die. You need quick reverse for that.

The correct way to wire it would be with drum switch between the converter and the lathe motor. If it's a big lathe it would need a reversing starter. If it has a foot brake/bar, it needs to be wired with an interlock so it doesn't start back up when the brake is released.
 
*-I think he will eventually burn up the motor manually getting it running.

Any three phase motor can be jury rigged as a phase converter however it isn't the same as an actual rotary phase converter with capacitors. You can take a three phase motor and rig it with a belt to a single phase motor to get it turning and then turn on single phase 220 and the motor will run without the single phase start motor. Then if it is wired to the three phase machine the machine will start and run but it will lack a lot of power. I have a rotary phase converter and it has capacitors to get it running and also capacitors to bump up the power on L3 to 220V. This compensates for the lack of power from single phase and makes the machine run close to having actual three phase.
 

You need to go ahead and try starting the ''idler'' in the other direction and let us know the result.

I wouldn't be surprised if that reversed the lathe motor, but I wouldn't bet more than a cup of coffee on that!
 
I don't know enough to argue for or against you.
The story I got from my friend Paul was he bought the RPC for practically nothing from a real old guy who was moving to a nursing home and selling off the last of his machinery. The rpc was nearly the last thing to go because it was so crude a way to start it that no one wanted it. The old guy said he had been using it that way for 25 years. Paul took a chance because it came with a good 3 ph breaker panel and fused 1 ph knife switch to power it.
Figured he'd use it till it dies then replace it. That was a couple of years ago and he uses it almost daily.
That's all I know.
 

I have a 14" lathe that someone put a 3 speed vehicle transmission on. The transmission is driven with a V-belt + single phase motor, the transmission has a pair of V-belts that drive the lathe. The lathe has a back-gear, so that gives it 6 speeds
+2 reverse.
I bought it used many years ago.

Dusty
 
Agree with you for reversing 3 phase, simple. Also be careful if it is a screw on chuck. Quick reversing or heavy loads in reverse can unscrew the chuck. And you don't want that!
 
Youtube machinist "doubleboost" has a rotary phase converter and as he is in the UK and running a metric lathe, needs to reverse his lathe when cutting Imperial threads.

In his videos you can hear him turn off the converter and turn it back on, then the lathe runs in reverse. I assume he is starting the converter in reverse to make the lathe run in reverse.
 

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